Conventional rocking bicycles have been known in which each driving shaft of a front wheel and rear wheel is eccentrical with the central axis of each wheel, and thus the wheels can be shaken up and down during running.
FIG. 1 is a side view showing an example of a conventional rocking bicycle, which is disclosed in a Korean Utility Model Registration Publication No. 183508 in the name of the same applicant as that of this invention.
Referring to FIGS. 2 and 3, a corresponding eccentric wheel apparatus for a rocking bicycle will be described below. A front drive wheel 10 having a center Sa located at a position distant by a certain distance from a circumferential center of a rear wheel (not shown) is connected with the rear wheel by means of a number of spokes 3 having different lengths. An intermediate wheel 40 is connected with a right-hand wheel 20 and a left-hand wheel 30 by means of a bolt 11. A number of chain sprockets 12 whose teeth become small sequentially from the concentrical axis with respect to a center 5a which is congruent with the center of a joint shaft 5 are connected with the outer surface of the right-hand wheel 20 located at a position of the center 5a. A shaft hole 12a whose center is congruent with the center 5a is formed on the center of the chain sprockets 12. An inner circumferential portion 21 having a certain height is protrudingly installed in the inner side of the right-hand wheel 20. A spur gear 22 having a certain pitch and a certain number of teeth is formed along the inner circumferential portion 21 in the inner side of the inner circumferential portion 21. A screw coupling unit 24 whose an inner side is formed of a female screw 23 is protrudingly installed at a certain position of the inner side surface of the right-hand wheel 20. A spring 25 giving an elastic force is wound around the outer circumferential portion of the screw coupling unit 24. The left-hand wheel 30 which is engaged with the screw coupling unit 24 protruded in the right-hand wheel 20 by means of a bolt 11 also includes a spur gear 22a having the same pitch and teeth as those of the spur gear 22 formed in the right-hand wheel 20 which is formed along an inner circumferential portion 31 in the inner side of the inner circumferential portion 31 of the left-hand wheel 30 in correspondence to the spur gear 22. The joint shaft 5 is inserted into the shaft hole 12a of the chain sprocket 12 formed in the right-hand wheel 20. The intermediate wheel 40 is installed between the right-hand wheel 20 and the left-hand wheel 30 to make the right-hand wheel 20 and the left-hand wheel 30 coupled with or separated from each other. A number of small or large spokes 3 are integrally installed in an outer circumferential portion 41 of the intermediate wheel 40. A spur gear 22b and a spur gear 22c which have the same tooth-shapes as those of the spur gears 22 and 22a are formed in the inner side of the outer circumferential portion 41 in correspondence to each other, in a manner that the spur gear 22 and the spur gear 22a which are formed in the right-hand wheel 20 and the left-hand wheel 30, respectively, can be engaged with each other. Accordingly, the spur gears 22, 22a, 22b, and 22c can be engaged with one another. The bolt 11 in the left-hand wheel 30 is screw-connected with the screw coupling unit 24 in the right-hand wheel 20. Bearings 6 and 6a are installed at the left and right ends of the joint shaft 5, respectively. Accordingly, the front drive wheel 10 in which the right-hand wheel 20, the intermediate wheel 40 and the left-hand wheel 30 are coupled with one another can be smoothly rotated according to rotation of the chain sprockets 12. A rear frame 4 is axially installed and screw-connected with nuts (not shown).
However, the conventional rocking bicycle having an eccentric wheel apparatus includes the right-hand wheel 20 and the left-hand wheel 30 which are engaged with the intermediate wheel 40 by means of the spur gears 22, 22a, 22b, and 22c to play a role of the front drive wheel 10, and assembled with one another by means of the bolt 11 and the screw coupling unit 24. Accordingly, since the right-hand wheel 20 and the left-hand wheel 30 should be engaged with each other centering on the intermediate wheel 40, a strong engagement force should be required for the right-hand wheel 20, the left-hand wheel 30, and the intermediate wheel 40. However, the tightening length of the bolt 11 is limited since the bolt 11 should be positioned at the inner side of a brake in view of the structures in thickness of the wheels, and thus the trifold engagement structure among the right-hand wheel 20, the left-hand wheel 30, and the intermediate wheel 40 cannot be firmly tightened. As a result, the trifold engagement structure may be released during running.
In addition, the spur gears 22, 22a, 22b, and 22c should be formed in the left-hand wheel 30, the inner side of the right-hand wheel 20, and both sides of the intermediate wheel 40, which pushes a production cost to rise. Further, since the assembly bolt 11 which assembles the left-hand wheel 30, the right-hand wheel 20, and the intermediate wheel 40 is small-sized, it may be released or lost. In this case, since the trifold engagement structure is broken, the wheels may be separated during running to thereby cause danger.